1. Field of the Invention
The invention relates to implantable prostheses. In particular, the invention relates to endoluminal stents and stent-grafts which are deployed in a blood vessel with the use of a delivery sheath. More particularly, the invention is related to a method and apparatus for loading the prosthesis into a delivery sheath.
2. State of the Art
An endoluminal stent-graft typically includes tubular graft material which is affixed to the inside or outside of a woven metallic stent. Endoluminal stent-grafts are most often used to repair blood vessels affected by a variety of lesions such as stenoses or aneurysms. The stent-graft is delivered to the damaged site of a blood vessel and is deployed using an introducer which tracks on a guide wire. The introducer preferably includes a delivery sheath and a plunger catheter. The stent-graft is placed in the delivery sheath where it is held in a radially compressed state. The introducer is delivered over the guide wire to the deployment site. With the sheath in position, the plunger catheter is used to push the stent-graft out of the sheath, whereupon the stent-graft self-expands.
Various methods and apparatus are used to load the stent-graft into the delivery sheath. One known method and apparatus for loading the delivery sheath was developed by one of the inventors herein and is shown in FIGS. 1-3. According to this method, a self-expanding stent-graft 10 is attached at one end 12 to one end 14 of a rod or tube 16 as shown in FIG. 1. The other end 18 of the rod 16 is inserted into the proximal end 20 of a delivery sheath 22 and pushed through the sheath until it exits the distal end 24 of the sheath 22 as shown in FIG. 2. The rod is pulled through the sheath 22 until the end 12 of the stent-graft 10 exits the distal end 24 of the sheath 22 as shown in FIG. 3, after which a measured length of the stent-graft 10 is cut leaving a measured length of the stent-graft 10 inside the sheath 22.
State-of-the-art stents and stent-grafts often have naturally flared ends which aid in the placement of the prosthesis and prevent the prosthesis from becoming dislodged or displaced after placement. In some cases, both ends of the stent are naturally flared. Ends which are naturally flared generally can be cut without adversely affecting the flare of the ends as the new end will take the same flare. Stents with naturally flared ends can be compressed to a non-flared state so they can be pushed through a delivery sheath without damaging the sheath or the ends of the stent. Some new stents and stent-grafts provided by the assignee hereof have at least one end which is "manually" flared (i.e. flared in a controlled manner by a specific manufacturing process). Stents of this type are disclosed in co-owned U.S. Pat. No. 5,632,772 and co-owned U.S. Pat. No. 5,628,788. The manually flared ends of these stents cannot be cut without losing the flare. In addition, these stents generally can only be pushed through a delivery sheath in one direction lest the sheath and/or the stent be damaged. It will be appreciated that the method and apparatus described above with reference to FIGS. 1-3 is not suitable for use with stents or stent-grafts which have a manually flared distal end as the orientation of the stent is important both for cutting and deployment purposes. As used herein, the "distal end" is used to refer to the end of the stent or stent-graft which is most distant from the practitioner and the term "proximal end" is used to refer to the end of the stent or stent-graft which is closest to the practitioner.